In order to erect a boiler, traditionally a main structure (main steel structure) is installed and then all the boiler components are sequentially installed one-by-one on and around the main structure.
Thus for example, the sequence could be main structure erection, installation of buckstays/headers and vertical heat exchanging walls at the upper part of the main structure, installation of internal heating surfaces (economizer, reheater, super heater), thus installation of the vertical heat-exchanging walls at the lower part of the main structure.
Then also the flue gas duct and other components such as piping, insulation, auxiliaries, cable trays, etc. are installed, typically outside of the main structure; these installations are carried out by lifting the component to be integrated into the boiler by a crane and connecting them to the required position. Usually the parts at the bottom are installed first and the parts at the upper part are then installed above the already installed parts at the bottom of the boiler.
The traditional method has the drawbacks that since the different components are one-by-one and sequentially installed, the boiler erection is very time consuming.